The word Agama means 'that which has come to (us)'. Tantra means 'that which protects with detail'. Sruti, the eternal word, is said to be of two forms – Nigama (Veda) and Agama. Two kinds of texts, Agama and Tantra are in general grouped under the same class of literature.

The Agamas are the primary source and authority for yoga methods and instruction. The Shaiva

Agamas revere the Ultimate Reality as Shiva (Shaivas). The Vaishnava-Agamas (Pancharatra and Vaikhanasas Samhitas) adore the Ultimate Reality as Vishnu (Vaishnavas). The Shakta-Agamas (Tantras) venerate the Ultimate Reality as Shakti the consort of Shiva and Divine Mother of the universe (Shaktas). Each set of texts expands on the central theological and philosophical teachings of that denomination.

The two main schools in the Vaishnava Agama are Pancharatra and Vaikanasa Agama. The Saiva Agama has led to the Saiva Siddhanta philosophy in South India and to the Pratyabhijna system of Kashmir Saivism. Smartas recognize the Agamas, but don't necessarily adhere to them, relying mainly on the smriti texts. In the Malay languages the word Agama literally means religion. The Agamas are also sometimes known as Tantras.

Agamas deal with the philosophy and spiritual knowledge behind the worship of the deity, the yoga and mental discipline required for this worship, and the specifics of worship offered to the deity. Each Agama consists of four parts. The first part includes the philosophical and spiritual knowledge. The second part covers the yoga and the mental discipline. The third part specifies rules for the construction of temples and for sculpting and carving the figures of deities for worship in the temples. The fourth part of the Agamas includes rules pertaining to the observances of religious rites, rituals, and festivals.

Elaborate rules are laid out in the Agamas for Silpa (the art of sculpture) describing the quality requirements of the places where temples are to be built, the kind of images to be installed, the materials from which they are to be made, their dimensions, proportions, air circulation, lighting in the temple complex etc. The Manasara and Silpasara are some of the works dealing with these rules. The rituals followed in worship services each day at the temple also follow rules laid out in the Agamas.

The Agamas state three essential requirements for a place of pilgrimage - Sthala, Teertham and Murthy. Sthala refers to the temple, Teertham, to the temple tank and Murthy to the deity(ies) worshipped. A temple may also be associated with a tree, called the Sthala Vriksham. For instance, the Kadamba tree at the Madurai Meenakshi Sundareswarar temple is the Sthala Vriksham. A lone banyan tree that adorns the spacious courtyard of the Ratnasabha at Tiruvalankadu is the Sthala Vriksham. The entire area is believed to have been a forest of banyan trees once........................................................................................................................................................................................

Classification of Agamas

They are a group of scriptures worshiping God in particular form and they describe detailed courses of disciple for the devotee. Like Upanishads there are many Agamas. They can be broadly divided into three sets of Agamas.

Vaikhanasas Samhitas – worship God as Lord Vishnu

Shaiva Agamas – worship God as Lord Siva

Shakta Tantras – worship God as Mother Goddess.

There is no Agamas for Lord Brahma (God of creation). Saktiates recoganizes 77 agamas. I am not sure about the actual number of the Vaishna Agamas. Vaishanavates consider Pancharatra Agamas as one of the most important agamas. Each Agama consists of Philosophy, mental discipline, Rules for constructing temples and Religious practices.

Smartas recognize the Agamas, but don't necessarily adhere to them, relying mainly on the smriti texts.

Vaishnava Agamas
The Vaishnava Agamas are grouped into four categories namely the Vaikhanasa, Pancharatra, Pratishthasara and Vijnanalalita. Of these, the Vaishanavites consider the Pancharatra Agama as the most important. These Agamas are believed to have been revealed by Narayana Himself. The Pancharatra Agama is again subdivided into seven sub agamas namely, the Brahma, Saiva, Kaumara, Vasishtha, Kapila, Gautamiya and the Naradiya. The Naradiya section of the Santi-Parva of the Mahabharata is the earliest source of information about the Pancharatras. Narada-Pancharatra says: "Everything from Brahman to a blade of grass is Lord Krishna." This corresponds to the Upanishadic declaration: "All this is, verily, Brahman—Sarvam Khalvidam Brahma."

The Pancharatra Agamas consider Vishnu as the Supreme Lord of the Universe and devotion to Vishnu as the sure path to liberation. According to another opinion, the Vaikhanasagama is the most ancient and most important Agama and all the Agamas practically and literally copied all their information from this sacred Agama. Tradition says that the Vaikhanasa Agama was originally compiled under the guidance of sage Vaikhanasa during the early Vedic period. Sri Madhavacharya held Pancharatra texts in high esteem and equated them with the Vedas and the epics, while Sri Shankaracharya had a different opinion.

There are two hundred and fifteen of these Vaishnava texts. Isvara, Ahirbudhnya, Paushkara, Parama, Sattvata, Brihad-Brahma and Jnanamritasara Samhitas are the important ones.

Saiva Agamas
Saivates have 28 principal Agamas and 108 Upa Agamas (minor agamas). Some of them date back to 2nd Century AD. Various schools of Saivas such as the Saiva Siddhantha school (the Southern Saivas), Tamil Saivas, Pratyabhijna system (Kashmiri Saivas) and Vira Saivas follow these texts and base their religious activity upon them and regard these Agamas as their authority, besides the Vedas.. The most prominent agama text in Saivas is the Kamika. These texts consider Siva as the Supreme Ruler of the Universe, the Highest Self, the Conscious Principle while Shakti is regarded as the unconscious or the natural principle who is the cause of bondage. The union of Shakti with Siva at the highest level leads to the freedom of the pasu (inner Self) from the Pasa or the attachment.

Sakta Agamas
The Followers of Saktas follow 27 Agamas also called Tantras. Saktas considers Sakti (the World-Mother) as the Supreme Self and relegates Iswara, the Divine Father, to a secondary position. In Saktas the Divine Mother is both the cause of delusion (maya) and the source of liberation.

They dwell on the Sakti (energy) aspect of God and prescribe numerous courses of ritualistic worship of the Divine Mother in various forms. There are seventy-seven Agamas. These are very much like the Puranas in some respects. The texts are usually in the form of dialogues between Siva and Parvati. In some of these, Siva answers the questions put by Parvati, and in others, Parvati answers, Siva questioning. Mahanirvana, Kularnava, Kulasara, Prapanchasara, Tantraraja, Rudra-Yamala, Brahma-Yamala, Vishnu-Yamala and Todala Tantra are the important works. The Agamas teach several occult practices some of which confer powers, while the others bestow knowledge and freedom. Sakti is the creative power of Lord Siva. Saktas is really a supplement to Saivism........................................................................................................................................................................................

Aspects of Agama

Agama deals with three phenomena, Mantra Yantra and Tantra.Mantra
Mantra is the sound-form of God-form and is often used synonymously to Devata. It is the means/basis for both Yantra and Tantra.

Yantra
Yantra is basically a contrivance, charged with the power of a mantra. It could be a geometric shape as in case of devata yantra or just any instrument as in case of an astra. It is the tool. The nature of Yantra depends on its purpose sought to be served.

Each devata is said to have a Yantra, a specific geometric shape that represents the nature of devata and a world model. For temporary purposes and worshipping, it could be drawn on clean floor with turmeric or some other powder, or for installations it could be carved on metal plates. The Yantra is worshipped and charged with corresponding mantra. It is treated like the devata, and is worshipped as the devata. The worship of yantra includes the worship of presiding Devata along with the consort, associate and subordinate Devatas and is an elaborate ritual consisting of propitiation of each of those.

Tantra
Tantra is the practitioner’s manual. It combines mantra, yogic methods and philosophy (Tatva-Mantra samanvaya). It elaborates procedures that a sadhaka should follow, at each stage of his sadhana.

Mantra, Yantra and Tantra are closely knit. Mantra is the energy. Yantras are geometric shapes that define the workings of various kinds of energies. Tantra deals with the philosophy and methods for redirecting and channelizing the energies to guide the spiritual evolution of the sadhaka.

Thus Tantra is the primary subject in Agamic literature. The word Tantra is in general used to refer to practices, and the subject dealing with those practices is called Tantra Sastra. To bring the spiritual knowledge of scriptures into the practitioner’s experience through well defined and time tested practices, is the essence of Tantra Sastra. For this reason, Tantra Sastra is variedly called Pratyaksha Sastra (the science of real experience), Sadhana Sastra (the science of spiritual practice) and Upasana Sastra. It has four parts or padas, jnana, yoga, kriya and carya........................................................................................................................................................................................

The Four Padas

Jnana Pada
Jnana pada deals with worldview and spiritual philosophy. It explains the nature of universe, cause of phenomenal world, creation and dissolution, eternal and transient principles of nature, the nature of self, the philosophy of binding and liberation.

Yoga Pada
Yoga Pada specifies methods for getting into experience the knowledge that Jnana Pada expounds. It contains the procedures to be followed, through which the individual consciousness can be united with the eternal consciousness whose nature is infinite bliss. Yogic sadhana is of two forms, Antaranga (inner) and Bahiranga (external). Their purpose is to purify one’s mind, words and deeds. One can bring about the evolution of the entire being through these two kinds of practices, through which the divine principle that pervades existence is realized. The purpose of Tantra Sastra is not to simply realize the divine, but to make life an instrument of the divine, to make every action follow the divine will. That is affected when the individual consciousness is united in the eternal consciousness. Yoga Pada expounds the methods for achieving that, based on Yoga Sastra and the science of consciousness.

Yoga is of different kinds, Laya, Kundalini and Mantra. The primary emphasis of Tantra Sastra is Kundalini Yoga, and the secondary emphasis is on Mantra Marga that forms basis for invoking the energy required for pursuing Kundalini Yoga. Faith and Devotion give the necessary support for the practitioner, to remain perseverant in the path.

Kriya Pada
Kriya Pada deals with the religious aspect such as temple construction, domestic and temple rituals, pilgrimage. It also gives procedures for worship, ritual codes and the ingredients of worship.

Carya Pada
Carya Pada contains the austerity, code of conduct, regulations to be followed during Diksha.
Agamas are primarily used by three religions – Vaishnava, Saiva and Sakta........................................................................................................................................................................................Veda and Agama
Agamic literature has many parallels to the Vedic texts; however the major difference is that in the Vedic discipline the different texts are classified based on the subjects they deal with. The various subjects like grammar, etymology, meter, phonetics, poetry, analysis, astronomy-astrology, ritual codes, moral codes, social organization, and consciousness studies are organized into different texts and arranged in a hierarchy as the ancillary texts of the Vedic discipline. Agamic texts in contrast, though they deal with various disciplines of knowledge, are primarily meant to be guides for practitioners. Many of the above subjects are referred to directly and indirectly, without expounding them but taking them for granted (for example grammar and etymology, chandas, varna-ashrama dharma etc) clearly making them part of the indigenous knowledge system rather than a parallel or equivalent knowledge system.

To draw a parallel between the subjects commonly dealt in the Vedic and Agamic texts,

The Jnana Pada of Agamic texts can be considered equivalent to the Upanishad portion of Veda and the Vedic Darsanas. However, the summary of spiritual philosophy of Veda is seen at the end of the Veda and in the worldviews based on the Veda, which shows evolution from Karma to Jnana. In Agamic texts it is the other way, the philosophy forms the basis for practice.

Kriya-Carya can be considered equivalent to the Srauta-Smarta portions of Kalpa, in that they prescribe the ritual code and general codes respectively. The temple and individual worship prescribed in Agama are equivalent to Srauta and Grihya rituals respectively. The temple itself is regarded as a replica of Yaga Sala.

Books on the Agamas
Among the existing books on the Agamas, the most famous are the Isvara-Samhita, Ahirbudhnya-Samhita, Sanatkumara-Samhita, Narada-Pancharatra, Spanda-Pradipika and the Mahanirvana-Tantra.